Production of disiloxanes



Patented Nov. 22, 1949 UNITED STATES PATENT Corning,

N. Y., assignors to Corning Glass Works, Corning,N. Y., a corporation ofNew York No Drawing. Application-February 21, 1946, Serial No. 649,386

Claims. (Cl. 269-4482) The present invention relates to new methods forthe preparation of unsymmetrical hexaorganodisiloxanes.

This application is a continuation-in-part of our co-pending applicationSerial No. 481,153, filed March 30, 1943, and assigned to the assigneeof the present invention, now abandoned.

The hexaorganodisiloxanes are a class of organosiloxanes in which twotriorganosubstituted silicon atoms are linked together by an oxygenatom, and in which the organic substituents are attached to the siliconby silicon to carbon bonds. This type of siloxanes has also beenreferred to as ethers and as triorganosilicon oxides. The symmetricalhexaorganodisiloxanes are known in the art, and may be prepared by thehydrolysis of triorgano silanes in which the silicon also carries ahydrolyzable group, such as a chlorine or alkoxy group. For example,hexaethyldisiloxane (CzHs) 3Si-O-Si(C2I-I5)s may be prepared by thehydrolysis of triethyl silicon chloride and condensation of thehydrolyzate. Other symmetrical hexaorganodisiloxanes may be preparedsimilarly as, for example, symmetrical tetramethyldiphenyldisiloxaneCal-I5 CH3) 2Si'O-Si (CH3) zCsHs' and hexamethyldisiloxane (CH3)3Si-O-Si (CH3) 3 For brevity in representation, radicals are abbreviated as follows: methyl as Me, ethyl as Et and phenyl as Ph.

The unsymmetrical hexaorganodisiloxanes are characterized by the twosilicon atoms of the molecule being differently substituted. Thus, anexample of this type of material is 1, 1, 3trimethyl-triphenyldisiloxane The unsymmetrical disiloxanes haveproperties similar to the symmetrical disiloxanes, and are adapted tothe same uses, such as temperature control and heat exchange media. Theyprovide a Wide range of materials for such'uses and may be employedeither alone or in mixture.

An object of the present invention is to provide methods for thepreparation of unsymmetrical hexaorganodisiloxanes.

In accordance with the present invention two diiferently substitutedsymmetrical hexaorganodisiloxanes, in which the organic groups areattached to silicon by carbon to silicon bonds, are interacted bymaintaining an alkali i'n intimate 2?. contact with a mixture of thBtWOrTheproduct of interaction contains substantial proportions ofunsymmetrical disiloxane in which the two silicon atoms are'substitutedas in the two symmetrical disiloxanes respectively-.-

In the present process, the-alkali which'is em ployed preferably is analkali-metal hydroxide, such as sodium or potassium hydroxidadue to thecommercial availabilityof these materials. Other strong alkalies, also,are-capable of effecting the present interaction such asthequater naryammonium hydroxides,-for example.benzyltrimethylammonium hydroxide: Theobtaining of the desired interaction of thedisiloxanes is not dependentupon the use of a critical amount of the strong alkali. Thus, it hasbeen found that siloxanes function ionically with as small amounts ofalkali as 7000 atoms of silicon per molecule of alkali andalso when thealkali present is more than equivalent to the silicon-present. It ispreferred, however, that the strong alkali be employed in amount lessthan equivalent to the silicon present (Na/SKI) though-'wi-th largeramounts the interactioncan be eii'ected by also having water present.The 'presencetof water prevents the entire mixture' from' goingoto saltsof the triorganosilanols, inasmuch as these salts are very readilyhydrolyzed.

Water may be present in any instance, though it is preferably limited inamount to notover 1.5 times the amount of alkali'employed, by weight, inorder to obtain rapid reaction:

Polar solvents such as alcohol maybe present, if desired, though theirpresence, or the amount thereof, is not critical in the present process.

The process hereof maybe eflected at room temperature or at eitherreduced or elevated temperatures, the primary difference being the rateof reaction. As is known, when the temperature of a siloxane issufliciently elevated, cleavage of some of the organo radicals from thesilicon atoms occurs. In case the process hereof is operated attemperatures suflicientlyeleva'ted to cause cleavage of this character,the resultant product contains some siloxanes which include diorganosiloxane units in mixture with unsymmetrical hexaorganodisiloxanes.These may be separated, if desired, by distillation or other suitablefractionation.

The process of the presentinventi'on isappltcable broadly to theinteraction of differently substituted hexaorganodisiloxanes. Since theactive portions of the molecules in the present process are thesilicon-oxygenjbonds, and-not the organic radicals, the processhereof isapplicable to siloxanes containing a wide variety of organo groups. Thegroups present may be alkyl radicals of, for example, 1 to 18 carbonatoms per alkyl; aryl radicals, such as phenyl, tolyl and xenyl; aralkylradicals, such as benzyl; alicyclic radicals, such as allyl andmethallyl. The siloxanes employed may contain a number of differentsubstituents. Thus, the process hereof is applicable to the interactionof symmetrical tetramethyldiphenyldisiloxane with hexamethyldisiloxaneto produce pentamethylphenyldisiloxane.

The reaction product is a mixture of disiloxanes. This mixture willcontain portions of the reactants together with the unsymmetricaldisiloxane which is produced. In order to obtain the unsymmetricaldisiloxane in purified form,

the alkali in the reaction mixture may be eliminated by neutralizationor otherwise and the disiloxanes separated, as by distillation.

The reaction involved in the rearrangement with which the presentinvention deals is an equilibrium. The specific equilibrium in anyinstance will depend upon the particular reactants and upon the specificreaction conditions. Likewise, the reaction conditions including thereaction time determine the extent of interaction, i. e., the degree towhich equilibrium is approached. Thus, at short reaction times thepercent of unsymmetrical oxide produced will be lower than at longerreaction times. The fact that the present interaction is actually anequilibrium is demonstrated by the fact that the unsymmetricaldisiloxane can be disproportionated under identical reaction conditionsto those employed in its preparation, with the production of the twosymmetrical disiloxanes.

For a better understanding of this invention, reference may be had tothe following examples which should be considered only as illustrativeof the method hereof:

Example 1 A mixture was prepared of 7.2 parts by weight mol.) ofsymmetrical tetramethylidiphenyldisiloxane (B. P. 295 at 760 mm.) and20.3 parts (25 mol.) of hexamethyldisiloxane (B. P. 98.5 at 760 mm), onepart (.8 mol.) of potassium hydroxide and 23 parts of 95% ethyl alcohol.The mixture formed a single phase. The atomic ratio of silicon topotassium was 1721. The mixture was allowed to stand for 24 hours atroom temperature after which it was neutralized, washed, dried oversodium sulfate and distilled at atmospheric pressure. The first fractionwhich was obtained contained the excess hexamethyldisiloxane which wasemployed. Next, there was a plateau at 206 C. at 760 mm. where theunsymmetrical siloxane, pentamethylphenyldisiloxane, was distilled. Thisproduct was obtained in quantity sufl'icient to account for most of theinitial symmetrical tetramethyldiphenyldisiloxane, only a small portionof which remained unconverted. The unsymmetrical product wascharacterized by effecting rearrangement thereof to the two symmetricaldisiloxanes. This rearrangement of the siloxane bonds was effected byallowing a mixture of 4.9 parts of the unsymmetrical disiloxane, 0.12part of potassium hydroxide and parts of 95% ethyl alcohol to standhours. The mixture was then washed free of alcohol and alkali, dried anddistilled. The distillation curve indicated that one-half of theunsymmetrical disiloxane had been reconverted to the two differentsymmetrical disiloxanes.

4 Example 2 The procedure of Example 1 was repeated with the exceptionthat benzyltrimethylammonium hydroxide was substituted for the potassiumhydroxide. The ratio of silicon to hydroxide on an equivalent basis was64:1. In this instance the reaction mixture was allowed to stand for 16hours at room temperature. The same results were obtained in thisinstance as in Example 1.

Example 3 Unsymmetrical tetramethyldiphenyldisiloxane Me3SiOSiMePh2 wasprepared by mixing 75 parts by weight of symmetricaltetraphenyldimethyldisiloxane PhzMeSi-O-SiMePhz, 175 parts ofhexamethyldisiloxane Me3Si--OSiMea, 7.8 parts of sodium hydroxide, and77 parts of ethyl alcohol. The mixture was refluxed at 70 C. for twodays, after which the clear solution was decanted from solids which hadsettled. The clear solution was then refluxed with water to hydrolyzeany sodium salts which might be present. The mixture was then allowed tostand at room temperature, whereupon a small amount of solid separated,which was removed by filtration. The filtrate was washed with diluteacid and water until neutral, dried with sodium sulfate, filtered anddistilled. There was first obtained a cut, amounting to 127 parts, whichwas the excess hexamethyldisiloxane and which had a boiling point of98.0-08.5". The next fraction obtained contained 70.7 parts boilingbetween and 135 at 2.5 to 3.5 mm. There remained 6 parts of stillresidue, there having been some mechanical loss in the operation. Thesecond cut was redistilled to obtain the desired tetramethyl- 1,1diphenyldisiloxane which was found to have a boiling point of 129-129.5C. at 3.5 mm. and 124.5 to C. at 2.5 mm. Upon analysis this material wasfound to contain 19.38% and 19.42% Si (calculated for (Col-I5)2CH3SiO-Si(CI-I3) 3 Si=19.59%). This compound had a melting point of 60to 65 C. and was stable under relux at 285 C. at atmospheric pressure.

I claim:

1. The method of preparing a hexaorganodisiloxane, which comprisesinteracting two differently substituted hexaorganodisiloxanes in whichthe organic groups are selected from the group consisting of alkyl andmonocyclicaryl radicals, said radicals being attached to the silicon bycarbon to silicon bonds, in intimate contact with an alkali metalhydroxide, whereby shifting of the triorgano silicon groups occurs withformation of a hexaorganodisiloxane which contains triorgano silicongroups corresponding to the triorgano silicon groups of the two reactingdisiloxanes.

2. The method of preparing an unsymmetrical hexaorganodisiloxane inwhich the organic radicals are selected from the group consisting ofalkyl and monocyclicaryl radicals, said radicals being attached to thesilicon by carbon to silicon bonds, which comprises interacting twodifferently substituted symmetrical hexaorganodisiloxanes in intimatecontact with an alkali metal hydroxide, whereby an unsymmetricalhexaorganodisiloxane is formed in which the two triorgano silicon groupscorrespond to the triorgano silicon groups in the two reactingdisiloxanes respectively.

3. The method defined in claim 2, in which the alkali metal hydroxidecontained in the reaction mixture is eliminated and the unsymmetricalhexaorganodisiloxane is separated from residual unreactedhexaorsanodisiloxanes.

4. The method of preparing unsymmetrical hexaorganodisiloxanes in whichthe organic radicals are selected from the group consisting of alkyl andmonocyclicaryl radicals, said radicals being linked to the silicon bycarbon silicon bonds, which comprises interacting two differentlysubstituted symmetrical hexaorganodisiloxanes in intimate contact withan alkali metal hydroxide, whereby an unsymmetrical hexaorganodisiloxaneis formed in which the two triorgano silicon groups correspondrespectively with the triorgano silicon groups in the two reactingdisiloxanes respectively, there being present less than 1 equivalent ofalkali metal hydroxide per equivalent of silicon.

5. The method of preparing unsymmetrical hexaorganodisiloxanes in whichthe organic radicals are selected from the group consisting of alkyl andmonocyclicaryl radicals, said radicals being linked to the silicon bycarbon to silicon bonds, which comprises interacting two diiferentlysubstituted hexaorganodisiloxanes in intimate contact with alkali metalhydroxide whereby an unsymmetrical hexaorganodisiloxane is formed inwhich the two triorgano silicon groups correspond with the triorganosilicon groups in the two reacting disiloxanes respectively, and in thepresence of water not in excess of 1.5 times the amount of alkali metalhydroxide by weight, there being less than 1 equivalent of alkali metalhydroxide per equivalent of silicon.

JAMES FRANKLIN HYDE. WILLIAM HERBERT DAUDT.

6 REFERENCES CITED The following references are of record in the file ofthis patent:

5 UNITED STATES PATENTS Number Name Date 2,258,218 Rochow Oct. 7, 19412,258,220 Rochow Oct. 7, 1941 2,258,222 Rochow Oct. 7, 1941 2,386,441Daudt Oct. 9, 1945 2,398,187 McGregor et a1 Apr. 9, 1946 2,421,653 SauerJune 3, 1947 FOREIGN PATENTS 15 Number Country Date 552,640 GreatBritain Apr. 19, 1943 OTHER REFERENCES

